The knee is a biomechanical mechanism whose function is dependent upon the restraints provided by the ligaments, capsule, menisci and bone geometry. The principle role of the ligaments and capsule is to maintain proper alignment between the tibia and femur by resisting undesirable joint displacements. In cases of ligament injury malalignment and instability occur which result in loss of function. The ability to reliably diagnose ligament injuries is currently limited by lack of detailed knowledge about function of individual ligaments as well as how they work together to restrain joint motions. The three-dimensional restraints provided by the passive soft tissues and bone geometry will be measured in human cadaveric knee preparations. Controlled displacements which simulate clinical laxity tests will be applied with an electro hydraulic testing system. The net reaction force and moment are measured with a six component dynamometer. Load-displacement data are acquired pre and post cutting selected ligaments. The difference between the tests describes the response of the cut ligament to the applied displacements. The contribution of the major ligaments and capsular structures to joint stiffness and compliance (laxity) are calculated from the data. An analytical model of the knee will be developed which incorporates th experimental ligament load-elongation relations. The model is used to investigate the effects of ligament injuries on joint laxity under loading conditions which simulate both clinical laxity tests and selected functional activities which cannot be readily studied in the laboratory. The bones are described as frictionless rigid constraints whose geometry is determined from three cadaveric preparation. The soft tissues are modeled as non-linear tension bands. The model output gives the displacement of the tibia with respect to the femur when a known load is applied to the tibia.